A technology has been known in which: cameras installed in a vehicle capture images of surroundings of the vehicle; and an amount of movement of the vehicle is obtained based on changes in the images (see Japanese Patent Application Publication No. 2008-175717). Japanese Patent Application Publication No. 2008-175717 aims at obtaining the amount of movement of the vehicle accurately even when the vehicle moves slightly at slow-speed. To this end, a feature point is detected from each image; the position of the feature point on the image is obtained; and thereby, the amount of movement of the vehicle is obtained from a direction and a distance of movement (amount of movement) of the feature point.
If, however, the feature point is detected under a bad condition, it is difficult to accurately obtain the amount of movement of the vehicle from the position of the feature point.